1. Field of the Invention
The present invention relates to a radar horn antenna and, more particularly, to a radar horn antenna that is mounted on a vehicle and detects an object.
2. Description of the Related Art
Hitherto, on-vehicle radar used in automatic drive and collision prevention of a vehicle has a disadvantage that it is difficult to detect an echo from a target due to reception of radio waves reflected from a road surface, i.e., due to influence of so-called ground clutter, depending on radiation pattern of a transmission/reception antenna and on how the radar antenna is mounted on the vehicle.
The Japanese Patent Publication (unexamined) No. 2001-201557 proposed a countermeasure to overcome such ground clutter incidental to the on-vehicle radar. In this known countermeasure, the radar antenna transmitting and receiving radio waves is accommodated in a casing for fixing the radar antenna, and a radome (cover) for protecting the radar antenna from hit stone, rain, snow, etc. is disposed at the front side of the radar antenna. The radar sensor constructed as described above is fixed onto the vehicle with a metal bracket. Lower portion of the metal bracket is provided with a shielding member projecting forward from a lower portion of the radar sensor. The shielding member reflects and attenuates side lobe radiated from the radar antenna, and this makes it possible to reduce ground clutter caused by the side lobe.
However, in the conventional on-vehicle radar of foregoing structure, a problem exists in that the radar becomes large and heavy as a whole. Moreover, another problem exists in that any desired radiation pattern is disturbed by radio waves reflected from the shielding member projecting forward at the lower portion of the radar antenna.